I do have frequent knee problems because of Suwari Waza. However, I don't believe that Suwari Waza by itself is really hard on the knees. Several years of Judo and 2 car accidents have damaged my knees to a certain extent, and I feel that Suwari Waza just reminds my knees of these sleeping injuries and brings back my old pains.

I would be curious to know of any knee injuries directly linked to Aikido practice (not previous injury).